Scanner systems for acquiring an image of an object, such as a printed circuit board, are well known in the arts of imaging and automated optical inspection. Some conventional scanner systems include sensors comprising a linear array of sensor elements. Other conventional scanner systems include sensors comprising a two dimensional array of sensor elements. Some systems employing two-dimensional array of sensor elements have been configured, for example, to operate in a time delay integration (TDI) mode of operation to acquire and image of an object. Other system employing a two-dimensional array of sensor elements have been configured to acquire a sequence of non overlapping images of an object.
TDI systems are well known in the art of optical scanning. In such systems, a sensor array is scanned over an object, such as a printed circuit board, by moving either the array or the object in a direction perpendicular to the rows of the array. The scanning speed and an array clock are synchronized so that in each column of the array, multiple sensor elements in sequence capture light from the same point on the object. Charge is accumulated between rows as the sensor array passes over the object so that sensor signals in each column are summed for each point on the object, thereby providing an image of the object with enhanced signal/noise ratio.
Common TDI sensors are based on charge-coupled device (CCD) technology, which allows the sensor signals to be summed by transferring charge along each column of the sensory array such that newly accumulated charge is added to charge having accumulated in previous rows of the column. Other TDI systems based on photodiode arrays, such as CMOS sensor arrays, are also known in the art.
U.S. Pat. Nos. 5,750,985 and 5,909,026, the disclosures of which are incorporated by reference, both describe sensors that can be employed in a TDI type arrangement.
Applicants' copending U.S. patent application Ser. No. 10/141,988, filed on May 10, 2002 and entitled “Optical Inspection System Employing a Staring Array Scanner”, the disclosure of which is incorporated by reference, describes an inspection system employing a two dimensional sensor array.